1. Field of the Invention
This invention relates to the field of manufacturing sound-absorbent materials, and, more particularly, to a method for treating polyimide foam by compression.
2. Description of the Related Art
In co-pending U.S. patent application Ser. No. 09/296,632, filed Apr. 22, 1999, a panel for absorbing acoustic energy is described. The disclosure of that application in hereby incorporated by reference.
In the referenced application, a sound absorbing panel of foamed polyimide is described, together with the utility and industrial applicability thereof. The method described therein of manufacturing the sound absorbent panels, describes the known method of manufacturing single panels. This is a time consuming and laborious operation, resulting in panels of higher cost than would be preferred, since the panels are manufactured individually.
In the previously disclosed method, a bun of polyimide foam is prepared in traditional fashion. This bun has standard dimensions of approximately 50xe2x80x3 widexc3x97100xe2x80x3 long and approximately 30xe2x80x3 high. According to the known method of manufacture, this bun is permitted to cure in a container having an open top, so that the cured bun has a rounded top, much like a loaf of bread. According to the known method of manufacturing panels, this bun is then cut into panels having the desired cross section. Each such panel is then conditioned individually. This conditioning consists of compressing a 3xe2x80x3 sheet of material from about 50% to about 75% of its uncompressed height, and thereby produce a densified foam that has an increased density of approximately 7-20%. A panel so conditioned provides increased acoustic absorption.
This method of manufacture has some drawbacks. First, it is time consuming to condition each sheet individually, and it would be advantageous to condition larger quantities of foam.
In addition, since the conditioning process occurs after the foam is cut into its desired shape, it may not have the precise dimensions desired for its ultimate goal, since it will be slightly compressed from its original shape. While it is possible under this prior method to approximate the resultant compressed dimensions, it would be preferable to have more precisely configured sheets utilized in the ultimate application.
Finally, it would be preferred if larger quantities of foam could be conditioned so that larger and differently shaped panels could be produced, which is not possible when foam is processed in smaller quantities.
Accordingly, there is a need in the art for a method for processing and conditioning larger quantities of polyimide foam for use in acoustic absorption.
In accordance with the invention, there is provided a new method of treating foam in a bun.
In a preferred embodiment of the invention, the method comprises compressing roughly half a bun of polyimide foam at a rate of no more than 12 feet per minute from its initial height of approximately 15xe2x80x3, until it reaches a compressed height of no more than 2xe2x80x3. The compression is maintained on the half-bun for no more than one minute, and then released. The bun is then permitted to expand, and it will rebound to approximately 90-95% of its initial height. This conditioned foam may then be cut or otherwise formed into acoustical panels of varying heights and/or configurations, without worry about the ultimate shrinkage after treatment. In addition the treated half-bun may be cut into irregular shapes of more varying dimensions, up to the maximum dimension of the treated half-bun.
In a preferred embodiment of the invention, the compression of the treated half-bun will take place at a speed of approximately 5 feet per minute.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.